The identification of petri dishes and especially covered petri dishes which have received an aliquot of a nutrient, generally prior to innoculation with the microorganisms to be cultured therein and incubation, is important because identification of the culture medium and of characteristics of the project is vital to a proper evaluation of the results obtained and failure of proper identification may lead to a significant misinterpretation of results and time-comsuming procedures for analyzing them.
Such petri dishes generally have a flat bottom and an upwardly flaring circumferential wall rising from this bottom to a limited height. A cover, having a downwardly flaring circumferential wall or skirt, generally rests loosely on the upper rim of the wall of the bottom member with the skirt terminating above the bottom of the covered dish. Both members are composed generally of a transparent or glass-clear synthetic resin and can be injection molded or otherwise formed so as to be disposable.
Apparatus for the labeling of petri dishes onstream has been proposed heretofore, such apparatus applying indicia to the cover or upon the bottom of the petri dish, or as a label which is adhesively attached to the bottom or to the cover.
All such systems have various disadvantages.
Marking the bottom, for example, is frequently ineffective because the bottom of a petri dish in normal handling can become soiled, e.g. with the nutrient medium, so as to make the markings illegible.
Marking of the covers is unsatisfactory because the covers may be removed and various covers may become intermingled so that identification of the culture media in respective petri dishes can no longer be assured.
Adhesive labels may become loose and fall off during incubation or handling.
Consequently, the need for effective marking of petri dishes in an onstream automatic manner has not been satisfactorily resolved heretofore.